specifically in Warsaw and would being fluent in both English and Polish be of any large advantage.
If you're able to do sales, especially big-ticket sales, the world is your oyster. The sky is the limit for any highly effective salesperson who speaks both languages at native level.
Otherwise, working in Poland is probably going to be a lot less financially rewarding than working in the UK, at least at your level. To the point where very few people would be tempted. Remember that it is not the gross or net income that is important as much as the savings potential, the amount of money you can put away in your bank account at the end of the month. In that respect, Poland lands far, far short of the UK.
That might change once you get abundant experience. But you are probably better off getting that experience in the UK than in Poland, if only for the savings potential.
If by "non-work related reasons" you mean a girl, then think twice. Nothing kills love quicker than lack of cash, and in your case, the steep opportunity costs you will be incurring will sting a lot, possibly to the point where you will resent having made such a great sacrifice and where that will taint any relationship.
As far as matters of the heart go, the advice I often give is that if it does not make sense in dollars and cents, then it probably makes no sense at all. If she won't move to the UK to be with you, then you might have to consider cutting you losses and find a more suitable mate. Better now at the early stages so that it hurts less and you both can start looking for someone else with little trouble.